Rolling mills



Oct. 31, 1961 w. c. F. HESSENBERG Re. 25,075

ROLLING MILLS Original Filed Jan. 25, 1955 QN\ 0 M x /9 O N\ QQ 0 NNQ 1l N VENT OR ask/ck flirjiwiifi M4 PR5!) (Ea/L Fr:

Al IORNEY United States Patent 25,075 ROLLING MILLS Wilfrid CecilFrederick Hessenberg, Bromley, England,

nssignor to The British Iron & Steel Research Associatlon, London,England Original No. 2,851,911, dated Sept. 16, 1958, Ser. No. 483,910,Jan. 25, 1955. Application for reissue Sept. 13, 1960, Ser. No. 55,815Claims priority, application Great Britain Jan. 26, 1954 Claims. (Cl.80-32) Matter enclosed in heavy brackets appears in the original patentbut forms no part of this reissue specification; matter printed initalics indicates the additions made by reissue.

This invention relates to rolling mills, particularly for steel. Rollingmills may be so arranged that the rolled material is passing through anumber of individual roll stands at the same time. The continuous stripmill in which the strip passes simultaneously through several standsarranged in tandem is a well known example. One of the objects ofcontinuous rolling is to produce long lengths of material having adesired cross-section which varies as little as possible from one end tothe other. In a tandem strip mill changes in thickness may occur as theresult of disturbances in one or more of the roll stands and it isdesirable that these should be corrected before the material issues fromthe last stand. An object of this invention is to provide a method forachieving this.

It is a characteristic of continuous mills that, unless the material isallowed to accumulate between the stands or is subjected to increasingand finally destructive tensile stresses, the rate in volume units persecond at which material leaves one stand must equal the rate at whichit enters the next. It is also well known that in the rolling of metalstheir density is not appreciably affected by the deformation theyreceive. It is therefore possible to state that in a continuous millwhere the material neither accumulates nor is subjected to increasingtension between the stands, the volume of material passing any point ina given time is the same for all points throughout the system. In thespecial case of a wide strip mill where the width of the strip is notaffected by rolling, the thickness of the strip multiplied by the speedof the strip will yield the same product at any point. This product isthe output of the mill.

The present invention employs the above features to provide apparatusfor measuring the issuing thickness of strip from a rolling mill and forcontrolling the mill to maintain a strip thickness at a desired value.Thus, according to the present invention, in a method of measuring thethickness of strip leaving a rolling mill, the outgoing thickness isderived from measurement of the speed and thickness of the strip priorto passage out of the mill and of the speed of the strip leaving themill. For a multi-stand mill, the speed and thickness is measuredbetween any two adjacent stands so that the output can be derived; theoutput is then compounded with the speed of the strip leaving the millto give an indication of the issuing strip thickness.

The invention includes apparatus for maintaining at the desired valuethe thickness of wide strip leaving a multi-stand rolling millcomprising means for producing signals in accordance with the speed (vand the thickness (h,) of the strip between two adjacent stands of themill, means for producing a signal in accordance with the speed of thestrip (v leaving the mill, means for compounding the said signals toproduce a resultant signal, representing the issuing thickness, inaccordance with Re. 25,075 Reissued Oct. 31, 1961 and means controlledby the resultant signal for maintaining the issuing thickness at thedesired value.

The invention will be more readily understood by way of example from thefollowing description of a continuous multi-stand steel rolling mill,reference being made to the accompanying drawing which is a schematicrepresentation of the mill.

In the drawing, the rolls of the stands of the mill are indicated at12a, 12b, 12c, etc., it being understood that the mill may have as manystands as may be desirable. Between any two adjacent stands, there arelocated a micrometer 13 which gives an electrical signal on the outputlines 14 in accordance with the thickness of the strip 15 between thosestands, and a device for giving an electric signal proportional to thelinear speed of the strip as it passes between the stands. This deviceconsists of adisc 16 mounted on the rotor of a tachometric generator 17,the arrangement being such that the plane of the disc 16 is aligned withthe direction of motion of the strip 15 and the disc rotates at the sameperipheral speed as the strip. The micrometer 13 and the device 16, 17are shown between the last two stands of the mill, but it will beunderstood that they may be located between any two other stands.

A second device for measuring the speed of the strip is located at theissuing side of the last roller stand 12a. This device is similar to thedevice 16, 17 and comprises a disc 18 in frictional contact with thestrip and carried on the motor of a tachometric generator 19.

The mill is provided with the customary reeling drum 20 for the strip,the reeler motor 21 and a driving motor 22 and screw-down motor 23 foreach of the roller stands; the driving motor 22 drives the rolls,whereas the screw down motor 23 causes adjustment in the initial settingof the work rolls 12 in relation to one another.

The output of generator 19 appearing at lines 24 is applied across anarcuate potentiometer 25. The signal appearing between the slider 26 ofthe potentiometer and one end of the potentiometer is applied in seriesopposition to the output from generator 17 to the input of a high gainamplifier 27, the output from which is connected to a light motor 28.The rotor shaft of motor 28 carries the slider 26 of potentiometer 25and also the slider 29 of a second arcuate potentiometer 30. Theelectric signal appearing on the output lines 14 of micrometer 13 isapplied across potentiometer 30 and the signal appearing on the slider29 and one end of the potentiometer is proportional to the outgoingthickness of the strip and an indication of that thickness can be givenby connecting the two points to a meter 31.

Alternatively, a signal may be derived proportional to the deviation ofthe issuing thickness from a given value by connecting slider 29 and oneside of the potentiometer 30 in series opposition to a source of voltageindicated in the drawing as a battery 32 connected across thepotentiometer 33. The slider arm 29 is connected to the slider 34 ofpotentiometer 33 and the difierence voltage appears on lines 35.

In order to provide an automatic control system for maintaining theissuing thickness of the strip substantially at a given value determinedby the setting of the potentiometer 33, the signal appearing on lines 35may be applied to the reeler motor 21, as shown, or alternatively to anyof the screw-down motors 23 of the roll stands or to any of the drivemotors 22, as indicated in chain line.

The operation of the system is as follows. If the speed and thickness ofthe strip between stands 12a and 12b are v b and the speed and thicknessof the strip, as it leaves the mill, are v, and h;, then the voltageapplied across potentiometer 25 is V, proportional to v: and the voltageappearing between slider arm 26 and one end of the 3 potentiometer is kVwhere k is determined by the position of the slider on thepotentiometer. The voltage applied to the input of amplifier 27 istherefore proportional to (V kV where V; is proportional to v and as thegain of the amplifier 27 is large the angular position of rotor shaft ofmotor 28 will be n Y Vz V2 since at balance the input to the amplifierwill be very nearly zero. Thus, as the voltage applied acrosspotentiometer 30 is proportional to h the signal appearing at the slider29 and one end of the potentiometer 30 is proportional to and becausethe output for wide strip is constant along the whole length of thestrip and therefore h v =h v this signal is proportional to h theissuing thickness of the strip and the meter 31 will indicate thatthickness.

When used, the potentiometer 33 applies a constant voltage h inopposition to the voltage from potentiometer 30 and the signal appearingat output lines 35 is therefore h h, the deviation of the thickness froma given value. When this voltage is applied to control any of motors 21,22 or 23, the rolling mill will operate to maintain the output signal onlines 35 zero or, in other words, the issuing thickness of the strip atthe desired value h, determined by the position of the slider 34.

As will be appreciated, the system illustrated in the accompanyingdrawing enables the thickness or gauge of the strip leaving the mill tobe measured indirectly with the attendant advantage that the stripthickness is measured as it leaves the last roll stand and not at somedistance from that stand. This advantage is of particular value when thesystem is used for automatic control of the mill as it enablesirregularities in the thickness to be compensated immediately instead ofafter a time lag.

In another embodiment, the micrometer and the two speedometers areemployed as before, but in this case percentage variations are measured.The signals from the micrometer and speedometer located between thestands are compounded to give a resultant signal equal to the output (vh From this resultant signal is obtained a signal proportional to thepercentage variation of the output from a given value, the given valuecorresponding to a desired thickness. Similarly, the signal from thespeedometer measuring the speed of the issuing strip is modified to givea signal proportional to the percentage variation in the issuing strip[thickness] speed from the given value, again corresponding to thedesired thickness. The two percentage signals are applied in seriesopposition to give a dilference signal proportional to the percentagevariation of the issuing thickness of the strip from the desired value.This signal can be applied to the reeling motor or to the screw-down ordriving motors of the stands to compensate automatically for variationsin the thickness and to maintain that variation zero.

As a result of the adjustments in accordance with the percentagevariation signal, there will occur changes in the tensions in the stripbetween the stands, which will bring the whole system into a newequilibrium. Changes in the thickness arising anywhere in the mill willbe ofiset by the effects of these changes in tension on the stripthickness in such a way that there will be no resultant change in thethickness of the strip as it leaves the final stand.

What is claimed, is:

1. In a rolling mill having a motor operated final stand and at leastone motor operated preliminary stand, manually adjustable means for[controlling] setting the thickness of the strip issuing from said finalstand, first variable signal generating means responsive to the velocityof a partially finished strip supplied to said final stand,

second variable signal generating means responsive to the thickness ofsaid strip supplied to said final stand, third variable signalgenerating means responsive to the velocity of the strip issuing fromsaid final stand, and a signal correlating means responsive to thesetting of said manually adjustable means and all of said signalgenerating means, said correlating means [varying the speed of operationof said final stand motor so as to maintain the prodnot of the thicknessand velocity of said issuing strip constant to the product of thethickness and velocity of said supplied strip] controlling said mill toadjust the thickness of the strip issuing from said final standsubstantially to the value set by said manually adjustable means.

2. A rolling mill as set forth in claim I, wherein said signalcorrelating means comprises a motor having a rotor, the position of saidrotor being adjustable in response to changes in the [differencebetween] quotient of the signals produced by said first and third signalgenerating means, and a potentiometer having a slider coupled to saidrotor, said second signal generating means comprising a source ofvoltage across said potentiometer, [the difference in the signalsgenerated by said first and third signal generating means beingdetectable across said slider and one terminal of said potentiometer]the voltage drop across one terminal and said slider being applied inopposition to the setting of said manually adjustable means forcontrolling said mill.

3. A rolling mill as set forth in claim 2, further comprising a secondpotentiometer, said [first] third signal generating means beingconnected across said second potentiometer, said second potentiometerhaving a slider connected to said rotor and a high gain amplifierconnected [across one terminal and] to said slider of said secondpotentiometer, the voltage drop across one terminal and said slider ofsaid second potentiometer being applied [to the input of said high gainamplifier for controlling said final stand motor.] in opposition to thesignal from said first generating means to the input of said high gainamplifier, and the output of said amplifier controlling said motorhaving said rotor.

4. In a: rolling mill having a motor operated final stand, at least onemotor operated preliminary stand, and reeling means for drawing stripthrough said stands, manually adjustable means for setting the valuedesired for the thickness of the strip issuing from said final stand,first variable signal generating means responsive to the velocity of astrip supplied to said final stand, second variable signal generatingmeans responsive to the thickness of said strip supplied to said finalstand, third variable signal generating means responsive to the velocityof the strip issuing from sand final stand, and a signal correlatingmeans responsive to the setting of said manually adjustable means andall of said signal generating means, said correlating means controllingsaid reeling means to control the thickness of strip issuing from saidfinal stand substantially to the value set by said manually adjustablemeans.

5. In a rolling mill having a motor operated final stand, at least onemotor operated preliminary stand, reeling means for drawing stripthrough said stands, and means for controlling the separation of therolls of at least one of said stands, manually adjustable means forsetting the value desired for the thickness of strip issuing from saidfinal stand, first variable signal generating means responsive to thevelocity of a strip supplied to said final stand, second variable signalgenerating means responsive to the thickness of said strip supplied tosaid final stand, third variable signal generating means responsive tothe velocity of the strip issuing from said final stand, and a signalcorrelating means responsive to the setting of said manually adjustablemeans and all of said signal generating means, said correlating meanscontrolling said controlling means to adjust the thickness of the stripissuing from said final stand to the value set by said manuallyadjustable means.

6. In a rolling mill having a motor operated final stand, at least onemotor operated preliminary stand and reeling means for drawing stripthrough said stands, manually adjustable means for setting the valuedesired for the thickness of strip issuing from said final stand, firstvariable signal generating means responsive to the velocity of a stripsupplied to said final stand, second variable signal generating meansresponsive to the thickness of said strip supplied to said final stand,third variable signal generating means responsive to the velocity of thestrip issuing from said final stand, and signal correlating meansresponsive to the setting of said manually adjustable means and all saidsignal generating means, said correlating means automatically varyingthe speed of operation of one of the motors of one of said stands toadjust the thickness of the strip issuing from said final stand to thevalue set by said manually adjustable means.

7. In a rolling mill having at least one motor operated stand, anautomatic control system for maintaining the thickness of the strip at arequired value comprising means for measuring the thickness of the stripat the entry side of the stand and for generating a first signalrepresenting that thickness, means for generating a second signalrepresenting the quotient of the velocities of the strip at the twosides of the stand, correlating means controlled by the first and secondsignals for generating an error signal indicative of the departure froma required value of the thickness of the strip leaving the stand, andcontrol means controlled by the error signal for controlling thethickness of the strip leaving the stand.

8. In a rolling mill having at least one motor operated stand, reelingmeans for drawing strip through said stand, and means for controllingthe separation of the rolls of said stand, manually adjustable means forsetting the value desired for the thickness of the strip issuing fromthe stand, first signal generating means responsive to the thickness ofthe strip supplied to said stand for generating a first signalrepresenting that thickness, second generating means for generating asecond signal representing the quotient of the velocities of the stripat the two sides of the stand, correlating means responsive to saidmanually adjustable means and said first and second signals forgenerating an error signal indicative of the departure from said desiredvalue of the thickness of the strip leaving said stand, and means forapplying said error signal to said means controlling the separation ofsaid rolls, to maintain said error signal substantially zero.

9. In a rolling mill having at least one motor operated stand, reelingmeans for drawing strip through said stand and control means forcontrolling the reeling means, manually adjustable means for setting thevalue desired for the thickness of the strip issuing from said stand,

first generating means responsive to the thickness of the strip suppliedto said stand for generating a first signal representing that thickness,second generating means for generating a second signal representing thequotient of the velocities of the strip at the two sides of the stand,correlating means responsive to said manually adjustable means and saidfirst and second signals for generating an error signal indicative ofthe departure from said desired value of the thickness of the stripleaving the stand, and means for applying said error signal to saidcontrol means to maintain said error signal substantially zero.

10. In a rolling mill having at least one motor operated stand and meansfor drawing strip through said stand, first variable signal generatingmeans responsive to the velocity of strip supplied to said stand, secondvariable signal generating means responsive to the thickness of saidstrip supplied to said stand, third variable signal generating meansresponsive to the velocity of the strip issuing from the mill,correlating means responsive to all said generating means for generatingan error signal indicative of the departure from a required value of thethickness of the strip issuing from said mill control means forcontrolling the thickness of the strip issuing from said mill, and meansapplying said error signal to said control means.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS 1,977,619 Boyer Oct. 23, 1934 2,051,018 UmanskyAug. 11, 1936 2,137,611 Hetler Nov. 22, 1938 2264095 Mohler Nov. 25,1941 2,275,509 Dahlstrom Mar. 10, 1942 2,281,083 Stoltz Apr. 28, 19422,297,812 Stoltz Oct. 6, 1942 2,303,596 Zeitlin Dec. 1, 1942 2,332,272Shayne Oct. 19, 1943 FOREIGN PATENTS 533,162 Great Britain Feb. 7, 1941

